1. Field of the Invention
The present invention relates to a tag for notifying that an article the theft of the which is monitored is taken out without permission and to a method of mounting the tag.
2. Description of the Related Art
Conventionally, there is disclosed, as this type of antitheft tags, an antitheft tag arranged such that the resonant circuit section of a tag mounted on an article whose theft is monitored is in resonance with the radio wave having a particular frequency and transmitted from a radio wave transmitter, a separation sensing means senses whether or not the tag is separated from the article whose theft is monitored and a separation notifying unit controls a notifying sound output means based on the sensed output from the separation sensing means (Japanese Unexamined Patent Publication No. 8-185584). In the antitheft tag, the resonant circuit section is composed of conductive metal foils having a predetermined shape which are formed on both the sides of an insulting dielectric thin film by etching or the like. For example, a dielectric circuit portion and a capacitor circuit portion are formed on the front surface of the thin film as a front surface flat pattern. The dielectric circuit portion is composed of a conductive metal foil and formed to a swirl shape, and the capacitor circuit portion is formed so as to continue to the center of the swirl of dielectric circuit portion. The separation sensing means is a removal sensing switch having an actuating lever which projects to the surface of the tag on which the tag is mounted. A power supply and a buzzer are electrically connected to the sensing switch. The separation notifying unit is a circuit composed of the removal sensing switch, the power supply and the buzzer which acts as the notifying sound output means. When the tag is mounted on the article, the actuating lever is pressed by the article, whereby the removal sensing switch is turned off. Whereas, when the tag is removed from the article, the actuating lever projects, whereby the removal sensing switch is turned on.
Further, a transmitting antenna and a receiving antenna stand at a predetermined interval at the entrance and the exit of a shop where the article whose theft is monitored is sold. These antennas are electrically connected to a controller. The controller causes the transmitting antenna to transmit a radio wave having a frequency with which the resonant circuit section resonates as well as checks the signal level of the signal received by the receiving antenna at all times. Further, a speaker for issuing a warning is connected to the control output of the controller.
In the antitheft tag arranged as described above, when the article whose theft is monitored is going to pass between the transmitting antenna and the receiving antenna regardless of that the price for it is not paid, the receiving antenna receives a signal whose receiving level is modulated because the radio wave transmitted from the transmitting antenna is resonated by the resonant circuit section of the tag mounted on the article whose theft is monitored. As a result, the controller issues a warning from the speaker so that the taking-out of the article whose price is not paid can be checked. In contrast, when the tag is removed from the article, the sensing switch is turned on by the projection of the actuating lever and the buzzer is sounded. Thus, the theft of the article can be reliably monitored.
However, in the conventional antitheft tag, when the tag is mounted on an article whose surface is formed of a conductive material such as aluminum and the like or a ferromagnetic material such as a steel sheet and the like, the resonance frequency of the resonant circuit section is changed and the tag is not resonated sometimes as compared with a case that the tag is mounted on an article whose surface is formed of an insulating material and a non-magnetic material because the self-inductance of the resonant circuit section changes.
An object of the present invention is to provide an antitheft tag having a resonant circuit section whose resonance frequency does not change depending upon the material of the surface of an article whose theft is monitored and a method of mounting the antitheft tag.
Another object of the present invention is to provide an antitheft tag whose thickness can be reduced and which can be made at a low cost and a method of mounting the antitheft tag.